The invention relates to balun circuits and, more particularly, to multi-layer balun circuits for coupling between balanced and unbalanced lines or devices in an electronic system.
A balun is a device used for coupling an unbalanced line or device and a balanced line or device for the purpose of transforming signals from balanced to unbalanced or from unbalanced to balanced. In other words, the balun can be used to transform an unbalanced input signal to a pair of balanced output signals or, in the reverse situation, a pair of balanced input signals to an unbalanced output signal. The balun, for example, may interface an unbalanced input with a balanced circuit by dividing an input signal received at an unbalanced terminal equally between two balanced terminals and by providing a first output signal at one balanced terminal with a reference phase and a second output signal at the other balanced terminal with a 180-degree phase difference relative to the reference phase. Baluns are useful in a variety of circuits, and are widely used to couple transmitters or receivers to antennas for wireless communication.
In general, the invention is directed to techniques for transforming unbalanced signals to balanced signals and balanced signals to unbalanced signals with a balun, and a balun for performing such techniques. The balun may be particularly useful for coupling an antenna to a transmitter or receiver in a wireless communication system.
In accordance with the invention, a balun may comprise a first unbalanced component and a second unbalaniced component that may be electrically coupled to form an unbalanced balun structure. The unbalanced components may, for example, be electrically coupled to one another by a conductive via. At least one of the unbalanced components is further coupled to an unbalanced port. The unbalanced port provides a coupling between the unbalanced components and an unbalanced device, such as an antenna. The unbalanced components may comprise conductive elements, such as conductive strips, disposed on a dielectric layer.
The balun may further include a balanced balun structure that includes a first balanced component and a second balanced component. Each balanced component electromagnetically couples more than one side of an associated unbalanced component. Each of the balanced components may comprise, for example, conductive strips disposed on a dielectric layer. For example, a balanced component may include a first conductive strip disposed on the dielectric layer adjacent to a first side of one of the unbalanced components, and a second conductive strip disposed on the dielectric layer adjacent to a second side of the unbalanced component. The conductive strips may be electrically coupled to one another to form the balanced component. In this manner, each balanced component electromagnetically couples more than one side of an associated unbalanced component. Each of the balanced components is coupled to a balanced port. The balanced port provides a coupling between the balun and a balanced device, such as receive and transmit circuitry of a transceiver.
The balun may be disposed on multiple layers, e.g., to conserve surface area. For example, the first unbalanced component and the first balanced component may be disposed on a first layer and the second unbalanced component and the second balanced component may be disposed on a second layer. The layers of the balun may be stacked on top of one another within a multi-layer circuit structure. Alternatively, one or more other intervening layers of the multi-layer circuit structure may be stacked between the layers of balun. In some embodiments, however, the balun may be formed on only a single layer. The balun may be formed by any of a variety of fabrication techniques including chemical vapor deposition, sputtering, etching, photolithography, masking, and the like.
In operation, the unbalanced components receive an unbalanced signal via the unbalanced port. The balun divides the received signal equally between the balanced ports. In particular, the electromagnetic coupling between the balanced components and the associated unbalanced components induces signals on the balanced components. The signals induced on the balanced components are transmitted to a balanced device via the balanced ports.
The signals output on each of the balanced ports are identical except for an approximate 180-degree phase shift. For example, the signal output from one of the balanced ports may have a first phase and the signal output from the other balanced port may have a second phase that is approximately 180-degrees out of phase relative to the phase of the signal output from first balanced port. Signal flow also may occur in the opposite direction. The balanced components may receive balanced signals from corresponding balanced ports, which may be coupled to transmit circuitry of a transceiver or transmitter. The electromagnetic coupling between the balanced components and the unbalanced components induces a signal on the unbalanced components. The signals on the unbalanced components are combined and output via the unbalanced port.
In one embodiment, the invention provides a balun comprising an unbalanced balun structure having a first unbalanced component and a second unbalanced component electrically coupled to one another and a balanced balun structure having a first balanced component and a second balanced component. The first balanced component electromagnetically couples more than one side of the first unbalanced component and the second balanced component electromagnetically couples more than one side of the second unbalanced component.
In another embodiment, the invention provides a method comprising forming a first unbalanced component, forming a first balanced component in an orientation for electromagnetic coupling with more than one side of the first unbalanced component, electrically coupling the first balanced component to a first balanced port, forming a second unbalanced component, electrically coupling the first and second unbalanced components, forming a second balanced component in an orientation for electromagnetic coupling with more than one side of the second unbalanced component, and electrically coupling the second balanced component to a second balanced port.
In a further embodiment, the invention provides a balun comprising a first unbalanced conductive element disposed on a first layer, a first balanced conductive element disposed on the first layer and oriented for electromagnetic coupling with a first side of the first unbalanced conductive element, a second balanced conductive element disposed on the first layer and oriented for electromagnetic coupling with a second side of the first unbalanced conductive element, wherein the first and second balanced conductive elements are electrically coupled to a first balanced port, a second unbalanced conductive element disposed on a second layer, wherein the first and second unbalanced conductive elements are electrically coupled, a third balanced conductive element disposed on the second layer and oriented for electromagnetic coupling with a first side of the second unbalanced conductive element, and a fourth balanced conductive element disposed on the second layer and oriented for electromagnetic coupling with a second side of the second unbalanced conductive element, wherein the third and fourth balanced conductive elements are electrically coupled to a second balanced port.
In an additional embodiment, the invention provides an apparatus comprising an unbalanced balun component and a balanced balun component that includes a first balanced element and a second balanced element disposed on opposite sides of the unbalanced component.
The invention may provide one or more advantages. Forming the balun on multiple layers can reduce cross talk between the unbalanced components of the balun. Further, forming the balun on multiple layers may reduce the amount of planar space needed for the balun. Further, the configuration of the balun significantly reduces the insertion loss of the balun. In particular, a balanced component can be formed to electromagnetically couple two or more sides of the unbalanced component. The configuration of the balun also allows the balun to be manufactured in low-temperature co-fired substrates and high temperature co-fired substrates having balanced component to unbalanced component spacing that is smaller than balanced component to unbalanced component spacing normally achieved in other types of manufacturing, such as printed circuit board manufacturing. However, printed circuit board manufacturing techniques may be used to construct the balun. Also, a length and width of the unbalanced and balanced components may be adjusted to achieve a desired impedance transformation in addition to conversion between balanced and unbalanced signals. Further, because the unbalanced components of the balun are electromagnetically coupled on more than one side, the amount of energy lost from the signal during electromagnetic coupling is reduced.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.